<?php
abstract class Unit{
	//得分
	abstract function bombardStrength();


	/*function addUnit(Unit $unit){
		throw new UnitException(get_class($this)." is a leaf");
	}

	function removeUnit(Unit $unit){
		throw new UnitException(get_class($this)." is a leaf");
	}*/

	function getComposite(){
		return null;
	}
}